It is an SA turbulence model and the discrete adjoint computed exactly with AD. Certainly the grids are highly stretched in the BL since the grids are resolving the viscous sublayer (y+ < 1) and the Reynolds numbers are on the order of 10's of millions. I tend only to see this behaviour at higher mach numbers when stronger shocks start to appear. For example, the adjoint system may solve fine at M=0.80, and fail to converge at M=0.85. For these RANS cases, the non-linear solution is solved using only RK with multigrid.
It is entirely possible a different preconditioner may not help at all, but there's not much else you can do. Gaetan On Mon, Apr 29, 2013 at 10:31 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote: > Gaetan Kenway <gaetank at gmail.com> writes: > > > For the forward solve I use ASM+ILU in the same manner as for the adjoint > > problem. > > The ASM not a bottleneck per se. Typically we see the adjoint problem > > taking the same amount of time as the non-linear problem for well-behaved > > flows, and the adjoint is shorter for less well-behaved flows. > > Sounds reasonable. > > > The real problem I am having is for certain RANS cases, the > > frozen turbulence adjoint is extremely difficult to solve --- requiring > > GMRES subspace sizes on the order of 400-500 to converge. > > Hmm, which turbulence model are you using? Is it related to stretched > grids? Continuous or discrete adjoint? > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130429/ded86ace/attachment.html>
